Centrifugal blood pump impeller and flow path

ABSTRACT

An impeller and rotor structure for a magnetically levitated pump define a smooth primary flow path and U-shaped secondary flow path, which extends around an annular magnetic rotor. The u-shaped secondary flow path is defined by a large outer side gap along an outer surface of the rotor, a large bottom gap along a bottom surface of the rotor and a large inner gap along an inner surface of the rotor. Shroudless impeller blades are purely radial and overhung from a thin peripheral ring attached to the annular magnetic rotor. A center post having a low aspect ratio extends through the annular rotor. The low aspect ratio is configured to prevent flow in the primary flow path from colliding directly with flow in the secondary flow path at the inner radial gap.

CROSS-REFERENCE TO RELATED APPLICATION DATA

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/013,204 filed on Jun. 17, 2014 entitled Centrifugal Blood PumpImpeller and Flow Path which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The present disclosure relates to centrifugal pump structures and moreparticularly to centrifugal magnetic levitation blood pump structures.

BACKGROUND

Heart disease is the leading cause of death for both men and women. Morethan five million Americans have heart failure and the number is stillon the rise. Blood pumps are effective in treating heart failure, butcan also cause side effects such as blood cell damage (hemolysis) andblood cell clotting (thrombosis).

Hemolysis and thrombosis can be primarily attributed to high shearstress and flow stagnation inside the blood pump. Early generation ofblood pumps were known for causing thrombosis due to shaft seals orcontact bearings between the rotating components such as rotors and thestationary components such as stators. Later hydrodynamic bearingseliminated the direct contact between the rotor and the stator by usingblood as the lubricant. However, high shear stress created inside thinfilms in the later pumps is a major source of hemolysis. More recentlydeveloped blood pumps include magnetic bearings in which magnetic forcessuspend the rotor in the blood with large gaps between the rotor and thestator and thus can greatly reduce the shear stress. However the morerecent blood pump designs with magnetic bearings include extracomponents, double-shrouded impellers and with magnets embedded insidethe shroud. The extra components and shrouded impellers can addsubstantial weight and size to this type of blood pump.

SUMMARY

A magnetic levitation pump apparatus according to an aspect of thepresent disclosure includes an annular magnetic rotor and an impellercoupled to the magnetic rotor. The impeller includes a flat peripheralring including a first surface coupled to the annular magnetic rotor, asecond surface facing away from the annular magnetic rotor and a centralcircular aperture concentrically aligned with the annular magneticrotor. A number of blades extend from the peripheral ring inwardlytoward an axis of rotation of the annular magnetic rotor. Each of theblades includes a blade root surface facing the annular magnetic rotorand located in a first plane normal to the axis of rotation, and a bladetip surface facing away from the annular magnetic rotor and located in asecond plane normal to the axis rotation. The blade root surface in thefirst plane and the blade tip surface in the second plane define apurely radial inducerless characteristic of the plurality of blades.

A magnetic levitation pump apparatus according to another aspect of thepresent disclosure includes housing portion having a center post and anannular cavity concentric with the center post. An annular magneticrotor is located in the annular cavity. A secondary flow path in theannular cavity includes a U-shaped cross-section and extends around theannular magnetic rotor. The secondary flow path is defined by a firstgap between the annular magnetic rotor and an outer surface of theannular cavity, a second gap between the annular magnetic rotor and abottom surface of the annular cavity, and a third gap between theannular magnetic rotor and an inner surface of the annular cavity.According to an aspect of the present disclosure, the first gap, thesecond gap and the third gap are substantially equal.

Another aspect of the present disclosure includes a method for reducingcell damage in a blood pump. The method includes directing blood througha primary flow path from an axial inlet cannula to a peripheral voluteof a magnetic levitation blood pump. The method further includesdirecting a portion of the blood through a constant gap U-shapedsecondary flow channel surrounding an annular magnetic rotor in themagnetic levitation blood pump.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the subject mattersought to be protected, there are illustrated in the accompanyingdrawings embodiments thereof, from an inspection of which, whenconsidered in connection with the following description, the subjectmatter sought to be protected, its construction and operation, and manyof its advantages should be readily understood and appreciated.

FIG. 1 is an illustration of a magnetic levitation pump apparatusaccording to aspects of the present disclosure.

FIG. 2 is an illustration of in impeller of a magnetic levitation pumpapparatus according to aspects of the present disclosure.

FIG. 3 is an illustration of a housing portion and impeller of amagnetic levitation pump apparatus according to aspects of the presentdisclosure.

FIG. 4 is an illustration of a volute and diffuser portion of a magneticlevitation pump apparatus according to aspects of the presentdisclosure.

FIG. 5 is an illustration of a primary flow path and a secondary flowpath in a magnetic levitation pump apparatus according to aspects of thepresent disclosure.

FIG. 6 is a process flow diagram illustrating a method for reducing celldamage in a blood pump according to aspects of the present disclosure.

It should be understood that the comments included in the notes as wellas the materials, dimensions and tolerances discussed therein are simplyproposals such that one skilled in the art would be able to modify theproposals within the scope of the present disclosure.

DETAILED DESCRIPTION

While aspects of the present disclosure include embodiments in manydifferent forms, there is shown in the drawings, and will herein bedescribed in detail, a preferred embodiment of the invention with theunderstanding that the present application is to be considered as anexemplification of the principles of the disclosure and is not intendedto limit the broad aspect of the disclosure to embodiments illustrated.

Aspects of the present disclosure include an impeller and rotorstructure and a secondary flow path arrangement that facilitatesconstruction of a smaller lighter safer blood pump. The disclosed pumpapparatus reduces the maglev pump weight and size compared to atraditional maglev pump and alleviates its side effects, namelyhemolysis and thrombosis. According to aspects of the presentdisclosure, an inducerless over-hung impeller is integrated on anannular motor rotor. The annular rotor is suspended by a total magneticbearing to define a uniform U-shaped secondary flow path beneath theimpeller.

Referring to FIG. 1, a pump apparatus 100, according to an aspect of thepresent disclosure includes a center post 102 a nose cone 104 extendingfrom the center post 102. The center post 102 is substantiallycylindrical and has a low aspect ratio such that the diameter of thecenter post 102 is substantially greater than its height. The low aspectratio post is configured to prevent a primary inlet flow in an axialinlet 126 from flowing directly into an opposing secondary path flow atthe periphery of the center post 102. The nose cone 104 has a two partprofile including a curved central portion matching an internalcurvature of the housing 118 and an external flat portion providing aconstant clearance between the nose cone and an impeller 116.

An annular rotor 106 is located in a circular channel around the centerpost 102. According to an aspect of the present disclosure, thethickness of the annular rotor thickness is about half its height sothat narrow U-shaped channel 108 is formed around the annular rotor 106.The narrow shape of the U-shaped channel 108 reduces the length ofbottom gap 110 relative to side gaps 112, 114 of the U-shaped channel108 which reduces chance of flow stagnation in bottom gap 110. Spacingbetween the bottom portion 122 of the housing 118, the annular rotor 106and the center post 102 defines the U-shaped secondary flow path 108with large gaps 110, 112, 114 which are all between about 0.010 inchesand 0.020 inches. In another example, according to an aspect of thepresent disclosure the large gaps 110, 112, 114 may be between about0.005 inches and 0.030 inches. Transitional portions of the secondaryflow path 108 between the side gaps 112, 114 and bottom gap 110 includea relatively large radius of curvature. Although the large gaps 110,112, 114 are shown as being three sides of a rectangular U-shapedchannel 108, aspects of the present disclosure include variations of theU-shaped channel 108, in which the bottom portion of the channel may becurved, and a bottom portion of the annular rotor 106 may also becurved. Such a curved configuration (not shown) may provide additionalbenefits, such as reduced disk pumping effects, for example.

A housing 118 of the pump apparatus 100 includes a top portion 120 and abottom portion 122. The top portion 120 includes an inlet cannula 124defining an axial inlet 126, a flat circular cover enclosing theimpeller, and a matching half volute. The bottom portion includes acylindrical housing structure which defines a partial volute, a flatcircular bottom, the cylindrical center post and nose cone 104.

Referring to FIG. 2, according to an aspect of the present disclosure,an impeller 116 includes a thin hub ring 202 attached to end of rotor106. The impeller includes a number of inducerless, i.e., purely radial,blades 204 extending from the hub ring 202. The blades 204 are semi-openand overhang a circular aperture defined by the hub ring 202. Accordingto an aspect of the present disclosure, a blade tip 206, shown as topedge, of each blade 204 is shroudless. A blade root 208, shown as thebottom edge, of each blade 204 is semi-open, such that a leading edge(inner) portion 210 is open and a trailing edge 212 (outer) portion ofeach blade 204 is covered by the hub ring 202.

Referring to FIG. 3 and FIG. 4, the volute 302 includes cone diffuser304 (FIG. 3) and cross section at proximal end 404 of cone diffuser 304includes a rectangular cross section portion 406 and a semi-circularcross section portion 408.

The inducerless blades 204 are purely radial, meaning the blade tip 206and root 208 are in two parallel planes normal to the pump rotatingaxis. According to the present disclosure, the blade leading edge 210 ofeach blade 204 is located at a diameter larger than the inner diameterof the inlet cannula 124 so that no axial-flow or mixed-flow elementoccurs at the leading edge portion 210 of the blades 204. Theinducerless blades 204 save weight and can potentially reduce theincidence-induced cell damage by delaying the turning of blood flow to alower speed.

According to aspects of the present disclosure the blade tips 206 areopen and shroudless. The shroudless configuration reduces the axialdimension and weight of the impeller 116 and further eliminatespotential flow stagnation between a rotating shroud and stationaryhousing. In an alternative configuration, the blade tips 206 may becovered by a shroud with no embedded magnets, for example. The bladeroot 208 is semi-open, such that the leading edge portion 210 of eachblade 204 is open and the trailing edge portion 212 of each blade iscovered by the hub ring 202 starting approximately mid way of the bladelength to the trailing edge of the blade.

According to an aspect of the present disclosure, the hub ring 202 isattached to the end of a magnet-filled annular rotor 106. Because thehub ring 202 and the annular rotor 106 are located at the outer edge ofthe impeller 116, the pump motor generates a larger torque and largerpower for a given speed as compared to more conventional centrifugalpumps. The increased torque and increased power of the disclosed rotorand impeller configuration allows reduction of magnet weight andreduction of rotor size for a given power specification.

According to another aspect of the present disclosure, the annular rotor106 and portions of the housing 118 form a U-shaped secondary flow path108 beneath the impeller 116. The annular rotor 106 is suspendedcompletely by a magnetic bearing such that relatively large gaps 110,112, 114 are formed along the entire secondary flow path 108. The largegaps 110, 112, 114 enhance wash with increased secondary flow to reducethrombosis and also produce lower shear stress to reduce hemolysis.

To construct an embodiment of a pump apparatus according to aspects ofthe present disclosure the radial blades 204 can be machined on anannular thin disk at the trailing edge portion of the blade roots 208 toform an inducerless overhung impeller 116. The impeller 116 can belaser-welded on one end of a magnet-filled annular rotor 106 to form arotor assembly. The rotor assembly can then be inserted into a bottomportion 122 of a housing 118 which includes a partial volute, a flatcircular bottom, the cylindrical center post 102 and nose cone 104. Atop portion 120 of the housing 118 includes an inlet cannula, a flatcircular cover, and a matching half volute can then be made to enclosethe impeller 116 and form the pump apparatus 100.

According to an aspect of the present disclosure, the nose cone 104profile and inner surface of the top portion 120 of the housing 118 forma smooth meridional flow path to gradually turn the flow from the axialinlet into the radial impeller. The nose cone 104 profile also includesa downstream flat section, which forms a constant axial clearancebetween the overhung blade roots 208 and the nose cone 104. Clearancebetween the nose cone 104 and the overhung blade roots 208 is similar tothe size of other gaps (0.005″-0.030″). The center post 102 may containcoils and other electronics configured to function as an active magneticbearing in a conventional manner in conjunction with permanent magnetsinside the annular rotor 106.

Referring to FIG. 4, according to an aspect of the present disclosure,the shape of the volute cross-section 402 is non-circular. The volutecross-section 402 includes a rectangular portion 406 combined with asemi-circular portion 408 to minimize the radial dimension withoutsacrificing the cross-sectional area. The semi-circular portion 408 canbe made as part of the top portion 120 of the housing 118 or part of thebottom portion 122 of the housing 118. A tangentially extendedcone-shaped diffuser 304 extends from the volute 302 at a location ofthe largest cross-section of the volute 302 and diverges from thehousing at an angle of about 6 degrees-8 degrees. The cone shapeddiffuser 304 serves as pump outlet and connects to an outflow graft.

According to an aspect of the present disclosure, the bottom portion 122of the housing 118 including the center post 102 and forms the U-shapedsecondary flow path 108 with the annular rotor 106 beneath the impeller116. The secondary flow path 108 includes the outer radial gap 114, thebottom axial gap 110 and the inner radial gap 112. Because nohydrodynamic bearings are involved, each of the gaps 110, 112, 114 canbe made relative large (0.005″-0.030″) when the annular rotor 106 islevitated by the magnetic bearing.

Referring to FIG. 5, an axial portion 502 of a primary flow path 500extends into the inlet cannula 124 and smoothly transitions around thenose cone 104 to a radial flow in a radial portion 504 of the primaryflow path 500. As static pressure rises along a passage space of theblades 204, a secondary flow in the secondary flow path 108 is pusheddownward in the outer radial gap 114, turns inward along the bottom gap110, flows upward in the inner radial gap 112 then reenters into thepassage space of the blades 204.

The large gaps, narrow aspect ratio and large corner radii of thesecondary flow path according to aspects of the present disclosure,reduce flow stagnation and shear stress in the secondary flow path andthereby reduce chances for thrombosis or hemolysis.

Referring to FIG. 6, a method 600 for reducing cell damage in a bloodpump according to aspects of the present disclosure includes directingblood through a primary flow path from an axial inlet cannula to aperipheral volute of a magnetic levitation blood pump at block 602 anddirecting a portion of the blood through a constant gap U-shapedsecondary flow channel surrounding an annular magnetic rotor in themagnetic levitation blood pump at block 604.

Although aspects of the present disclosure are described with respect tothe secondary flow channel or secondary flow path being defined withrespect to surrounding gaps which may be substantially equal, constantor uniform, it should be understood that aspects of the presentdisclosure may also include the secondary flow path being defined byunequal gaps or non-uniform gaps, for example.

As used herein, the term “coupled” or “communicably coupled” can meanany physical, electrical, magnetic, or other connection, either director indirect, between two parties. The term “coupled” is not limited to afixed direct coupling between two entities. The matter set forth in theforegoing description and accompanying drawings is offered by way ofillustration only and not as a limitation. While particular embodimentshave been shown and described, it will be apparent to those skilled inthe art that changes and modifications may be made without departingfrom the broader aspects of applicants' contribution. The actual scopeof the protection sought is intended to be defined in the followingclaims when viewed in their proper perspective based on the prior art.

What is claimed is:
 1. A magnetic levitation pump apparatus, comprising:an inlet cannula defining an axial inlet; an annular magnetic rotor; animpeller coupled to the magnetic rotor, the impeller includes: a flatperipheral ring including a first surface coupled to the annularmagnetic rotor, a second surface facing away from the annular magneticrotor, and a central circular aperture concentrically aligned with theannular magnetic rotor, and a plurality of blades extending from theperipheral ring inwardly towards an axis of rotation of the annularmagnetic rotor, wherein each of the blades includes: a blade rootsurface facing the annular magnetic rotor and located in a first planenormal to the axis of rotation, and a blade tip surface facing away fromthe annular magnetic rotor and located in a second plane normal to theaxis of rotation, wherein the blade root surface and the blade tipsurface are in parallel planes and define a purely radial inducerlesscharacteristic of the plurality of blades; and a nose cone portionextending through the central circular aperture of the flat peripheralring, wherein a curved central portion of the nose cone extends axiallybeyond the plurality of blades and into the axial inlet.
 2. Theapparatus of claim 1, wherein each of the blades further includes: atrailing edge portion coupled to the second surface of the flatperipheral ring; and a leading edge portion overhanging the centralcircular aperture of the flat peripheral ring.
 3. The apparatus of claim1, wherein the blade tip surface of each of blades is shroud-less. 4.The apparatus of claim 1, wherein the magnetic rotor includes magneticportions and non-magnetic portions.
 5. The apparatus of claim 1, furthercomprising: a housing portion including a center post and an annularcavity concentric with the center post, wherein the annular magneticrotor is located in the annular cavity.
 6. The apparatus of claim 5,further comprising: a secondary flow path in the annular cavity, thesecondary flow path having a U-shaped cross-section and extending aroundthe annular magnetic rotor from a first gap between the annular magneticrotor and an outer surface of the annular cavity, to a second gapbetween the annular magnetic rotor and a bottom surface of the annularcavity, and to a third gap between the annular magnetic rotor and aninner surface of the annular cavity, wherein the first gap, the secondgap and the third gap are between about 0.010 inches and about 0.020inches.
 7. The apparatus of claim 5, further comprising: a secondaryflow path in the annular cavity, the secondary flow path having aU-shaped cross-section and extending around the annular magnetic rotorfrom a first gap between the annular magnetic rotor and an outer surfaceof the annular cavity, to a second gap between the annular magneticrotor and a bottom surface of the annular cavity, and to a third gapbetween the annular magnetic rotor and an inner surface of the annularcavity, wherein the first gap, the second gap and the third gap arebetween about 0.005 inches and about 0.030 inches.
 8. The apparatus ofclaim 2, wherein the nose cone portion includes a substantially flatperipheral portion overlapping the leading edge portion of each of theblades and defining a constant gap between the nose cone portion and theblades.
 9. The apparatus of claim 8, wherein the curved central portionof the nose cone extends into the axial inlet and corresponds to aninternal curvature of the inlet cannula to define a substantially smoothspacing between the nose cone and the inlet cannula.
 10. The apparatusof claim 9, comprising: a volute extending partially around a peripheryof the impeller and in fluid communication with the axial inlet, whereinthe impeller and volute define a primary flow path.
 11. The apparatus ofclaim 7, wherein the third gap is located radially outward from thecurved central portion of the nose cone.
 12. The apparatus of claim 7,wherein the third gap is located radially outward from the inletcannula.